There are many theme repositories out there and some that put out pretty good work. I personally have always liked WooThemes. I remember when they started a while back thinking, “this should be good”, they have always had great design and code with the developer in mind.
There are really one a few reasons I choose Woo and they are rather simple.
As WordPress has grown so have the frameworks, but most of the time that just means more bloat and backwards compatibility. Some frameworks have their own maze of functionality that is damn near impossible to breakdown in less than a weeks worth of time. Woo keeps it simple with their themes and the code is right there in the theme files.
There is no shoratage of free themes out there, but honestly 90% are just garbage and not well supported. With WooThemes you get access to their amazing code, design and framework updates. At the price of free they are my goto themes when I have a friend in dire need of a fast, clean, usable install.
When WooThemes started they were a group of three with amazing designs. At the time they were constantly pushing the bounds of what WordPress could do. Back in 2008 there were a lot of boundaries to push! While most themes were focusing on blogs, Woo was putting full website theme as a very high quality. To this day their themes are some of the most simple clean designs I’ve seen on the web.
I took a little time posted a few screen shots for you to get a quick look. Download the pdf if you want to see it in better resolution. (PDF)